1. Field of The Invention
This invention relates to an electrostatic image-bearing dielectric member which is suitable for use in ionography.
2. Description of The Related Art
In recent years, there has been carried out, as one of copying or printing processes, an image-forming process using so-called ionography. The process comprises providing a support drum having a dielectric film thereon as an electrostatic image-bearing dielectric member, generating ions or charged particles by means of an ion generator to form an electrostatic image on the surface of the dielectric member, developing the thus formed electrostatic image with a toner, and transferring and fixing the developed image on a copying material.
The known dielectric member used in the ionography makes use of a porous anodized aluminum film as the dielectric layer. Since the porous anodized aluminum film has a multitude of fine pore openings, it is disadvantageous in that the wear resistance is poor and toner particles are liable to enter the pores thereby causing the image quality to be worsened. To avoid this, there has been proposed a method wherein after the formation of the porous anodized aluminum film, the film is subjected to adsorption with silane coupling agents and then impregnated with epoxy resins (Japanese laid-open Patent Application No. 63-294586). For sealing the pores of the porous anodized aluminum film, there is known a method which makes use of waxes as a sealant (Japanese Laid-open Patent Application No. 60-50083), or a method wherein polytetrafluoroethylene is impregnated (Japanese Laid-open Patent Application No. 61-193157).
Aside from the anodized aluminum film, the dielectric film has also been fabricated from a mixture consisting of inorganic powder, lubricants and film-forming resins (Japanese laid-open Patent Application No. 61-144651).
However, where the anodized aluminum film is adsorbed with silane coupling agents and impregnated with epoxy resins or is impregnated with epoxy resins containing silane couplers, there arises the problem that the surface hardness is not satisfactory and the relative dielectric constant is larger than about 7, so that satisfactorily high chargeability cannot be obtained. Moreover, after the adsorption and impregnation steps, additional steps of baking the resin and eliminating the surface layer of the resin are necessary, with the attendant problem that the procedure becomes complicated with a reduction in yield and reproducibility of film characteristics. Alternatively, where waxes or polytetrafluoroethylene are provided as a sealant and impregnated, chargeability and surface hardness are not satisfactory because they are very low, coupled with another problem that these materials do not provide adequate adhesion to the anodized aluminum film.
When the dielectric layer made of a mixture of inorganic powder, lubricants and film-forming resins, the dielectric layer becomes embrittled owing to the presence of the inorganic powder and the fabrication process becomes complicated, with the problem that the yield is reduced.